Ion exchangeable glass with fast diffusion

ABSTRACT

Glasses that undergo rapid ion exchange. The glasses comprise SiO2, Al2O3, P2O5, Na2O, K2O, and, in some embodiments, at least one of MgO and ZnO. The glass may, for example, be ion exchanged in a molten KNO3 salt bath in less than 1 hour at temperatures in a range from about 370° C. to about 390° C. to achieve a depth of surface compressive layer of greater than about 45 microns, or in a range from about 0.05t to about 0.22t, where t is the thickness of the glass. The glasses are fusion formable and, in some embodiments, compatible with zircon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/381,614 filed on Dec. 16, 2016, which claims the benefit of priorityunder 35 U.S.C. § 119 of U.S. Provisional Application Ser. No.62/268,659, filed Dec. 17, 2015, the contents of which are relied uponand incorporated herein by reference in their entirety.

BACKGROUND

The disclosure relates to ion exchangeable alkali aluminosilicateglasses. More particularly, the disclosure relates to alkalialuminosilicate glasses that undergo rapid ion exchange.

It has been found that the resistance of chemically strengthened glassesto damage during drop testing (i.e., dropping the glass from aprescribed height) is affected by the depth of the surface compressivelayer achieved by chemical strengthening. To date, glasses arechemically strengthened to the extent that the resulting central tensiondoes not exceed a limit beyond which delayed failure occurs.

However, it has also been found that for some glass compositionsmechanical properties increase with increasing central tension. Highlyfrangible glasses beak spontaneously with no delayed failure.

SUMMARY

Glasses that exhibit high diffusivity and undergo rapid ion exchange areprovided. These glasses comprise comprise SiO₂, Al₂O₃, P₂O₅, Na₂O, K₂O,and, in some embodiments, at least one of MgO and ZnO. The glass may,for example, be ion exchanged in a molten KNO₃ salt bath in less than 1hour at temperatures in a range from about 370° C. to about 390° C. toachieve a depth of surface compressive layer of greater than about 45microns, or in a range from about 0.05t to about 0.22t, where t is thethickness of the glass. The glasses are fusion formable (i.e., theliquidus temperature is less than the 160 kP temperature) and, in someembodiments, compatible with zircon (i.e., the zircon breakdowntemperature is greater than the 35 kP temperature of the glass).

Accordingly, an aspect of the disclosure is to provide a glasscomprising SiO₂, Al₂O₃, P₂O₅, Na₂O, K₂O, and optionally at least one ofMgO and ZnO, wherein (R₂O (mol %)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₃ (mol%))<0, where R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O and R′O=ZnO+MgO+CaO+SrO+BaO.

Another aspect of the disclosure is to provide an ion exchanged glasscomprising glass comprising SiO₂, Al₂O₃, P₂O₅, Na₂O, K₂O, and optionallyat least one of MgO and ZnO, wherein (R₂O (mol %)+R′O (mol %))−(Al₂O₃(mol %)+P₂O₃ (mol %))<0, where R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O andR′O=ZnO+MgO+CaO+SrO+BaO.

Another aspect of the disclosure is to provide a method of ionexchanging a glass. The method comprises: ion exchanging a glass in anion exchange bath comprising KNO₃ at a temperature in a range from about370° C. to 390° C. for a period of up to one hour. The glass comprisesSiO₂, Al₂O₃, P₂O₅, Na₂O, K₂O, and optionally at least one alkaline earthoxide and ZnO, wherein (R₂O (mol %)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₃(mol %))<0, where R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O andR′O=ZnO+MgO+CaO+SrO+BaO. The ion exchanged glass has a layer that isunder a compressive stress and extends from a surface of the glass to adepth of compression of at least about 45 μm.

According to a first aspect of the disclosure, a glass is provided. Theglass comprises: about 56 mol % to about 67 mol % SiO₂; Al₂O₃; about 4mol % to about 8 mol % P₂O₅; Na₂O; greater than about 1 mol % K₂O; andZnO, wherein (R₂O (mol %)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₅ (mol %))<0,R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O, and R′O=ZnO+MgO+CaO+SrO+BaO.

According to a second aspect of the disclosure, the glass of the firstaspect is provided wherein the glass has a coefficient of thermalexpansion of at least about 92×10⁻⁷° C.⁻¹.

According to a third aspect of the disclosure, the glass of the first orsecond aspects is provided wherein the glass has a compressive layerextending from a surface of the glass to a depth of compression of atleast about 45 μm.

According to a fourth aspect of the disclosure, the glass of the thirdaspect is provided wherein the depth of compression is in a range fromabout 45 m up to about 200 μm.

According to a fifth aspect of the disclosure, the glass of the third orfourth aspects is provided wherein the glass has a thickness t andwherein the depth of compression is less than or equal to about 0.22t.

According to a sixth aspect of the disclosure, the glass of any of thethird through fifth aspects is provided wherein the compressive layercomprises a compressive stress of at least about 500 MPa.

According to a seventh aspect of the disclosure, the glass of any of thethird through sixth aspects is provided wherein the glass has been ionexchanged in an ion exchange bath comprising KNO₃ at a temperature in arange from about 370° C. to about 390° C. for up to one hour.

According to an eighth aspect of the disclosure, the glass of any of thefirst through seventh aspects is provided wherein the glass has aliquidus temperature T^(L), a 160 kP temperature T^(160kP), a 35 kPtemperature T^(35kP), and a zircon breakdown temperature T^(breakdown),wherein T^(L)<T^(160P) and T^(breakdown)>T^(35kP).

According to a ninth aspect of the disclosure, the glass of any of thefirst through eighth aspects is provided wherein the glass comprises:about 57 mol % to about 67 mol % SiO₂; about 9 mol % to about 18 mol %Al₂O₃; about 13 mol % to about 16 mol % Na₂O; and greater than about 1mol % to about 5 mol % K₂O.

According to a tenth aspect of the disclosure, the glass of any of thefirst through ninth aspects is provided further comprising less thanabout 1 mol % MgO.

According to an eleventh aspect of the disclosure, the glass of any ofthe first through tenth aspects is provided wherein the glass comprisesgreater than 60 mol % SiO₂.

According to a twelfth aspect of the disclosure, the glass of any of thefirst through eleventh aspects is provided wherein R₂O+R′O is less thanabout 18 mol %.

According to a thirteenth aspect of the disclosure, the glass of any ofthe first through twelfth aspects is provided wherein the glass issubstantially free of MgO.

According to a fourteenth aspect of the disclosure, the glass of any ofthe first through thirteenth aspects is provided wherein the glass issubstantially free of at least one of B₂O₃ and lithium.

According to a fifteenth aspect of the disclosure, an ion exchangedglass comprising the glass of any of the first through fourteenthaspects is provided.

According to a sixteenth aspect of the disclosure, a consumer electronicproduct is provided, comprising: a housing having a front surface, aback surface and side surfaces; electrical components provided at leastpartially within the housing, the electrical components including atleast a controller, a memory, and a display, the display being providedat or adjacent the front surface of the housing; and the glass of any ofthe first through fifteenth aspects is disposed over the display.

According to a seventeenth aspect of the disclosure, a glass isprovided. The glass comprises: SiO₂; Na₂O; about 4 mol % to about 8 mol% P₂O₅;

about 9 mol % to about 18 mol % Al₂O₃; greater than about 1 mol % K₂O;and 0 mol % B₂O₃, wherein (R₂O (mol %)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₅(mol %))<0, R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O, and R′O=ZnO+MgO+CaO+SrO+BaO.

According to an eighteenth aspect of the disclosure, the glass of theseventeenth aspect is provided wherein the glass has a coefficient ofthermal expansion of at least about 92×10⁻⁷° C.⁻¹.

According to a nineteenth aspect of the disclosure, the glass of theseventeenth or eighteenth aspects is provided wherein the glass has acompressive layer extending from a surface of the glass to a depth ofcompression of at least about 45 μm.

According to a twentieth aspect of the disclosure, the glass of thenineteenth aspect is provided wherein the depth of compression is in arange from about 45 μm up to about 200 μm.

According to a twenty-first aspect of the disclosure, the glass of thenineteenth or twentieth aspects is provided wherein the glass has athickness t and wherein the depth of compression is less than or equalto about 0.22t.

According to a twenty-second aspect of the disclosure, the glass of anyof the nineteenth through twenty-first aspects is provided wherein thecompressive layer comprises a compressive stress of at least about 500MPa.

According to a twenty-third aspect of the disclosure, the glass of anyof the nineteenth through twenty-second aspects is provided wherein theglass has been ion exchanged in an ion exchange bath comprising KNO₃ ata temperature in a range from about 370° C. to about 390° C. for up toone hour.

According to a twenty-fourth aspect of the disclosure, the glass of anyof the seventeenth through twenty-third aspects is provided wherein theglass has a liquidus temperature T^(L), a 160 kP temperature T^(160kP),a 35 kP temperature T^(35kP), and a zircon breakdown temperatureT^(breakdown), wherein T^(L)<T^(160P) and T^(breakdown)>T^(35kP).

According to a twenty-fifth aspect of the disclosure, the glass of anyof the seventeenth through twenty-fourth aspects is provided wherein theglass comprises about 56 mol % to about 67 mol % SiO₂.

According to a twenty-sixth aspect of the disclosure, the glass of anyof the seventeenth through twenty-fifth aspects is provided wherein theglass comprises about 13 mol % to about 16 mol % Na₂O.

According to a twenty-seventh aspect of the disclosure, the glass of anyof the seventeenth through twenty-sixth aspects is provided wherein theglass comprises: about 57 mol % to about 67 mol % SiO₂; about 9 mol % toabout 18 mol % Al₂O₃; about 13 mol % to about 16 mol % Na₂O; and greaterthan about 1 mol % to about 5 mol % K₂O.

According to a twenty-eighth aspect of the disclosure, the glass of anyof the seventeenth through twenty-seventh aspects is provided furthercomprising less than about 1 mol % MgO.

According to a twenty-ninth aspect of the disclosure, the glass of anyof the seventeenth through twenty-eighth aspects is provided wherein theglass comprises greater than 60 mol % SiO₂.

According to a thirtieth aspect of the disclosure, the glass of any ofthe seventeenth through twenty-ninth aspects is provided wherein R₂O+R′Ois less than about 18 mol %.

According to a thirty-first aspect of the disclosure, the glass of anyof the seventeenth through thirtieth aspects is provided wherein theglass is substantially free of MgO.

According to a thirty-second aspect of the disclosure, the glass of anyof the seventeenth through thirty-first aspects is provided wherein theglass is substantially free of lithium.

According to a thirty-third aspect of the disclosure, an ion exchangedglass is provided comprising the glass of any of the seventeenth throughthirty-second aspects.

According to a thirty-fourth aspect of the disclosure, a consumerelectronic product is provided comprising: a housing having a frontsurface, a back surface and side surfaces; electrical componentsprovided at least partially within the housing, the electricalcomponents including at least a controller, a memory, and a display, thedisplay being provided at or adjacent the front surface of the housing;and the glass of any of the seventeenth through thirty-third aspectsdisposed over the display.

According to a thirty-fifth aspect of the disclosure, a method of ionexchanging a glass is provided. The method comprises: ion exchanging aglass in an ion exchange bath for a period of up to one hour to form anion exchanged glass, wherein: the ion exchange bath comprises KNO₃ andis at a temperature in a range from about 370° C. to 390° C., the glasscomprises: SiO₂, Al₂O₃, P₂O₅, Na₂O, and K₂O,

wherein (R₂O (mol %)+RO (mol %))−(Al₂O₃ (mol %)+P₂O₅ (mol %))<0,R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O, and R′O=ZnO+MgO+CaO+SrO+BaO, and the ionexchanged glass comprises a layer under a compressive stress, the layerextending from a surface of the ion exchanged glass to a depth ofcompression of at least about 45 μm.

According to a thirty-sixth aspect of the disclosure, the method of thethirty-fifth aspect is provided wherein the depth of compression is in arange from about 45 μm up to about 200 μm.

According to a thirty-seventh aspect of the disclosure, the method ofthe thirty-fifth or thirty-sixth aspects is provided wherein thecompressive stress is at least about 500 MPa.

According to a thirty-eighth aspect of the disclosure, the method of anyof the thirty-fifth through thirty-seventh aspects is provided whereinthe glass has a thickness t and wherein the depth of compression is lessthan or equal to about 0.22t.

According to a thirty-ninth aspect of the disclosure, the method of anyof the thirty-fifth through thirty-eighth aspects is provided whereinthe glass comprises: about 56 mol % to about 67 mol % SiO₂; about 4 mol% to about 8 mol % P₂O₅; Al₂O₃; Na₂O; greater than about 1 mol % K₂O;and ZnO.

According to a fortieth aspect of the disclosure, the method of any ofthe thirty-fifth through thirty-eighth aspects is provided wherein theglass comprises: SiO₂; Na₂O; about 4 mol % to about 8 mol % P₂O₅; about9 mol % to about 18 mol % Al₂O₃; greater than about 1 mol % K₂O; and 0mol % B₂O₃.

According to a forty-first aspect of the disclosure, the method of anyof the thirty-fifth through fortieth aspects is provided wherein theglass comprises greater than 60 mol % SiO₂.

According to a forty-second aspect of the disclosure, the method of anyof the thirty-fifth through forty-first aspects is provided wherein theglass further comprises up to about 1 mol % MgO.

According to a forty-third aspect of the disclosure, the method of anyof the thirty-fifth through forty-second aspects is provided whereinR₂O+R′O is less than about 18 mol %.

According to a forty-fourth aspect of the disclosure, the method of anyof the thirty-fifth through forty-third aspects is provided wherein theion exchanged glass comprises at least about 13 mol % Al₂O₃.

These and other aspects, advantages, and salient features of the presentdisclosure will become apparent from the following detailed description,the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a glass sheet that hasbeen ion exchanged.

FIG. 2A is a plan view of an exemplary electronic device incorporatingany of the glasses disclosed herein.

FIG. 2B is a perspective view of the exemplary electronic device of FIG.2A.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that, unless otherwise specified, termssuch as “top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, it is understood that the group maycomprise, consist essentially of, or consist of any number of thoseelements recited, either individually or in combination with each other.Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, it is understood thatthe group may consist of any number of those elements recited, eitherindividually or in combination with each other. Unless otherwisespecified, a range of values, when recited, includes both the upper andlower limits of the range as well as any ranges therebetween. As usedherein, the indefinite articles “a,” “an,” and the correspondingdefinite article “the” mean “at least one” or “one or more,” unlessotherwise specified. It also is understood that the various featuresdisclosed in the specification and the drawings can be used in any andall combinations.

As used herein, the terms “glass article” and “glass articles” are usedin their broadest sense to include any object made wholly or partly ofglass. Unless otherwise specified, all compositions are expressed interms of mole percent (mol %). Coefficients of thermal expansion (CTE)are expressed in terms of 10⁻⁷/° C. and represent a value measured overa temperature range from about 20° C. to about 300° C. using a push-roddilatometer in accordance with ASTM E228-11, unless otherwise specified.

As used herein, the term “liquidus temperature,” or “T^(L)” refers tothe temperature at which crystals first appear as a molten glass coolsdown from the melting temperature, or the temperature at which the verylast crystals melt away as temperature is increased from roomtemperature. The liquidus temperature of the glass is measured inaccordance with ASTM C829-81 (2015), titled “Standard Practice forMeasurement of Liquidus Temperature of Glass by the Gradient FurnaceMethod”. As used herein, the term “160 kP temperature” or “T^(160kP)”refers to the temperature at which the glass or glass melt has aviscosity of 160,000 Poise (P), or 160 kiloPoise (kP). As used herein,the term “35 kP temperature” or “T^(35kP)” refers to the temperature atwhich the glass or glass melt has a viscosity of 35,000 Poise (P), or 35kiloPoise (kP). The T^(160kP) and T^(35kP) may be determined inaccordance with ASTM C965-96(2012), titled “Standard Practice forMeasuring Viscosity of Glass Above the Softening Point”.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue. Thus, a glass that is “substantially free ofMgO,” for example, is one in which MgO is not actively added or batchedinto the glass, but may be present in very small amounts (e.g., ≤0.01mol %) as a contaminant.

Compressive stress and depth of compression (DOC) are measured usingthose means known in the art. Compressive stress (including surface CS)is measured by surface stress meter (FSM) using commercially availableinstruments such as the FSM-6000, manufactured by Orihara IndustrialCo., Ltd. (Japan). Surface stress measurements rely upon the accuratemeasurement of the stress optical coefficient (SOC), which is related tothe birefringence of the glass. SOC in turn is measured according toProcedure C (Glass Disc Method) described in ASTM standard C770-16,entitled “Standard Test Method for Measurement of Glass Stress-OpticalCoefficient,” the contents of which are incorporated herein by referencein their entirety.

As used herein, DOC means the depth at which the stress in thechemically strengthened alkali aluminosilicate glass article describedherein changes from compressive to tensile. DOC may be measured by FSMor or a scattered light polariscope (SCALP) depending on the ionexchange treatment. Where the stress in the glass article is generatedby exchanging potassium ions into the glass article, FSM is used tomeasure DOC. Where the stress is generated by exchanging sodium ionsinto the glass article, SCALP is used to measure DOC. Where the stressin the glass article is generated by exchanging both potassium andsodium ions into the glass, the DOC is measured by SCALP, since it isbelieved the exchange depth of sodium indicates the DOC and the exchangedepth of potassium ions indicates a change in the magnitude of thecompressive stress (but not the change in stress from compressive totensile); the exchange depth of potassium ions in such glass articles ismeasured by FSM.

Refracted near-field (RNF) method or SCALP may be used to measure thestress profile. When the RNF method is utilized to measure the stressprofile, the maximum CT value provided by SCALP is utilized in the RNFmethod. In particular, the stress profile measured by RNF is forcebalanced and calibrated to the maximum CT value provided by a SCALPmeasurement. The RNF method is described in U.S. Pat. No. 8,854,623,entitled “Systems and methods for measuring a profile characteristic ofa glass sample”, which is incorporated herein by reference in itsentirety. In particular, the RNF method includes placing the glassarticle adjacent to a reference block, generating apolarization-switched light beam that is switched between orthogonalpolarizations at a rate of between 1 Hz and 50 Hz, measuring an amountof power in the polarization-switched light beam and generating apolarization-switched reference signal, wherein the measured amounts ofpower in each of the orthogonal polarizations are within 50% of eachother. The method further includes transmitting thepolarization-switched light beam through the glass sample and referenceblock for different depths into the glass sample, then relaying thetransmitted polarization-switched light beam to a signal photodetectorusing a relay optical system, with the signal photodetector generating apolarization-switched detector signal. The method also includes dividingthe detector signal by the reference signal to form a normalizeddetector signal and determining the profile characteristic of the glasssample from the normalized detector signal.

The stress profiles may also be determined from the spectra of boundoptical modes for TM and TE polarization by using the inverseWentzel-Kramers-Brillouin (IWKB) method as taught in U.S. Pat. No.9,140,543, the contents of which are hereby incorporated by reference inits entirety.

Referring to the drawings in general and to FIG. 1 in particular, itwill be understood that the illustrations are for the purpose ofdescribing particular embodiments and are not intended to limit thedisclosure or appended claims thereto. The drawings are not necessarilyto scale, and certain features and certain views of the drawings may beshown exaggerated in scale or in schematic in the interest of clarityand conciseness.

Described herein is an ion exchangeable glass that is capable ofundergoing ion exchange of K⁺ ions for Na⁺ ions at a rate that isgreater than that of similar glasses. These glasses comprise P₂O₅ andK₂O and have very high diffusion rates at ion exchange temperatures. Thehigh rate of K⁺ diffusivity and K⁺ for Na⁺ ion exchange enables deepdepths of compression (DOC) to be achieved with less stress relaxationoccurring during the ion exchange.

The glasses described herein may comprise SiO₂, Al₂O₃, P₂O₅, Na₂O, K₂O,and optionally ZnO and/or at least one alkaline earth oxide R′O, where(R₂O (mol %)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₃ (mol %))<0, whereR₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O and R′O=ZnO+MgO+CaO+SrO+BaO. In someembodiments, the glass consists essentially of or comprises from about56 mol % to about 67 mol % SiO₂ (i.e., 56 mol %≤SiO₂≤67 mol %); fromabout 9 mol % to about 18 mol % Al₂O₃ (i.e., 9 mol %≤Al₂O₃≤18 mol %);from about 4 mol % to about 8 mol % P₂O₅ (i.e., 4 mol %≤P₂O₅≤8 mol %);from about 13 mol % to about 16 mol % Na₂O (i.e., 13 mol %≤Na₂O≤16 mol%); and greater than about 1 mol % to about 5 mol % K₂O (i.e., 1 mol%≤K₂O≤5 mol %). In certain embodiments, the glass consists essentiallyof or comprises from about 60 mol % to about 65 mol % SiO₂ (i.e., 60 mol%≤SiO₂≤65 mol %); from about 10 mol % to about 15 mol % Al₂O₃ (i.e., 10mol %≤Al₂O₃≤15 mol %); from about 4 mol % to about 7 mol % P₂O₅ (i.e., 4mol %≤P₂O₅≤7 mol %); from about 13 mol % to about 16 mol % Na₂O (i.e.,13 mol %≤Na₂O≤16 mol %); and greater than about 1 mol % to about 5 mol %K₂O (i.e., 1 mol %≤K₂O≤5 mol %).

In some embodiments, the glass is substantially free of MgO. In someembodiments, the glass is substantially free of at least one of B₂O₃,lithium, Li₂O. Compositions, strain points, anneal points, and softeningpoints of non-limiting examples of these glasses are listed in Table 1.

Silica (SiO₂) is the primary network former in the glasses describedherein. In some embodiments, these glasses comprise from about 56 mol %to about 67 mol % SiO₂. In certain embodiments, the glasses comprisefrom about 58 mol % or about 60 mol % to about 65 mol % SiO₂.

Alumina (Al₂O₃) primarily facilitates ion exchange. In addition, Al₂O₃suppresses phase separation. In some embodiments, the glasses describedherein include from about 9 mol % to about 18 mol % Al₂O₃. In otherembodiments, these glasses comprise 10 mol % to about 17 mol % Al₂O₃.

The presence of the alkali metal oxides Na₂O and K₂O increases the CTEof the glass. K₂O is also very effective in increasing the Na⁺ to K⁺diffusion between the glass and the molten salt ion exchange bath andplays a primary role in increasing CTE, followed by Na₂O. However, thepresence of K₂O tends to lower compressive stress when the glass is ionexchanged and lowers the temperature at which zircon breaks down(T^(breakdown)) in the presence of the glass melt. The glasses describedherein, in some embodiments, comprise greater than about 1 mol % K₂O. Insome embodiments, the glass comprises greater than about 1 mol % toabout 5 mol % K₂O and, in other embodiments, from about 2 mol % to about5 mol % K₂O. The presence of Na₂O in the glass enhances the ionexchangeability of the glass. In some embodiments, the glass comprisesfrom about 13 mol % to about 16 mol % Na₂O. The glass may, in someembodiments, further comprise other alkali metal oxides (Li₂O, Rb₂O,Cs₂O), but these oxides either inhibit ion exchange, result in lowersurface compressive stress in the ion exchange glass, or are relativelyexpensive. In some embodiments, the glass comprises less than about 1.5mol % Li₂O, and, in certain embodiments, is free of or substantiallyfree of Li₂O.

Zinc oxide and the alkaline earth oxide MgO increase the surfacecompressive stress in the ion exchanged glass. However, MgO tends toreduce the coefficient of thermal expansion of the glass. In someembodiments, the glasses described herein comprise up to about 1 mol %MgO and ZnO (i.e., MgO+ZnO≤1 mol %), or up to about 0.1 mol % MgO andZnO (i.e., MgO+ZnO≤0.1 mol %), or up to about 0.01 mol % MgO and ZnO(i.e., MgO+ZnO≤0.01 mol %). In certain embodiments, the glass is free orsubstantially free of MgO and/or ZnO. CaO tends to inhibit ion exchangeand decreases the CTE of the glass. Accordingly, the glass may be freeof CaO as well as SrO and BaO.

The glasses described herein are characterized by (R₂O (mol %)+R′O (mol%))−(Al₂O₃ (mol %)+P₂O₃ (mol %))<0, where R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂Oand R′O=ZnO+MgO+CaO+SrO+BaO. This relationship contributes, at least inpart, to the ability of the glasses to undergo rapid ion exchange. Insome embodiments, the total amount of alkali metal oxides (R₂O) and ZnOand alkaline earth oxides (R′O) in the glasses described herein is lessthan about 18 mol % (i.e., R₂O+R′O<18 mol %).

The presence of P₂O₅ in the glass promotes ion exchange of the glass byincreasing the diffusivity of certain cations such as, for example, K⁺.In addition, P₂O₅ tends to increase the temperature at which zirconbreaks down (T^(breakdown)) in the presence of the glass melt. In someembodiments, the glasses described herein comprise from about 4 mol % toabout 8 mol % P₂O₅ and, in certain embodiments, from about 4 mol % toabout 7 mol % P₂O₅.

The glasses described herein have coefficients of thermal expansion(CTE) of at least about 92×10⁻⁷° C.⁻¹. In other embodiments, the CTE isat least about 94×10⁻⁷° C.⁻¹ and in still other embodiments, at leastabout 96×10⁻⁷° C.⁻¹. In certain embodiments, the CTE is in a range fromabout 92×10⁻⁷° C.⁻¹ up to about 102×10⁻⁷° C.⁻¹, and, in otherembodiments, from about 92×10⁻⁷° C.⁻¹ up to about 100×10⁻⁷° C.⁻¹. Table1 lists coefficients of thermal expansion for non-limiting examples ofthe glasses described herein.

The glasses described herein are fusion formable; i.e., the glasses haveliquidus temperatures T^(L) that allow them to be formed by the fusiondraw method or by other down-draw methods known in the art. In order tobe fusion formable, the liquidus temperature of a glass should be lessthan the 160 kP temperature T^(160kP) of the glass (i.e.,T^(L)<T^(160kP)).

The hardware used in the fusion draw process, such as an isopipe, isoften made from zircon. If the temperature at which the zircon in theisopipe breaks down to form zirconia and silica (also referred to hereinas the “breakdown temperature” or “T^(breakdown),”) is less than anytemperature “seen” or experienced on the isopipe, the zircon will breakdown to form silica and zirconia. As a result, the glass formed by thefusion process will contain zirconia inclusions (also referred to as“fusion line zirconia”). It is therefore desirable to form the glass attemperatures that are too low to decompose zircon and create zirconia,and thus prevent the formation of zirconia defects in the glass.Alternatively, the isopipe may be made of other refractory materials,such as alumina, thus eliminating the breakdown of zircon as a factor inthe fusion draw process.

Because fusion is essentially an isoviscous process, the highesttemperature seen by the glass corresponds to a particular viscosity ofthe glass. In those standard fusion-draw operations known in the art,this viscosity is about 35 kP, and the temperature at which thisviscosity is attained is referred to as the 35 kP temperature, orT^(35kP). Table 2 lists density, T^(L), T^(160kP), T^(35kP), andT^(breakdown) for selected examples listed in Table 1.

In some embodiments, the glasses described herein are ion exchangedusing those means known in the art. In one non-limiting example, theglass is immersed in a molten salt bath containing an alkali metalcation such as, for example, K⁺, which is larger than the Na⁺ cationpresent in the glass. Means other than immersion in a molten salt bathmay be used to ion exchange of the glass. Such means include, but arenot limited to, the application of a paste or gel containing the cationto be introduced into the glass to at least one surface of the glass.

The ion exchanged glass has at least one surface layer that is under acompressive stress (CS), as schematically shown in FIG. 1. Glass 100 hasa thickness t, first surface 110, and second surface 112. Glass 100, insome embodiments, has a thickness t of up to about 2 mm, and all rangesand subranges therebetween, for example from about 0.1 mm to about 2 mm,up to about 1 mm, up to 0.7 mm, or up to about 0.5 mm. Glass 100 has afirst layer 120 under a compressive stress (“compressive layer”)extending from first surface 110 to a depth of compression d₁ into thebulk of the glass article 100. In the embodiment shown in FIG. 1, glass100 also has a second compressive layer 122 under compressive stressextending from second surface 112 to a second depth of compression d₂.Glass 100 also has a central region 130 that extends from d₁ to d₂.Central region 130 is under a tensile stress or central tension, whichbalances or counteracts the compressive stresses of layers 120 and 122.The depths of compression d₁, d₂ of first and second compressive layers120, 122 protect the glass 100 from the propagation of flaws introducedby sharp impact to first and second surfaces 110, 112 of glass 100,while the magnitude of the compressive stress in first and secondcompressive layers 120, 122 minimizes the likelihood of a flawpenetrating through the depth d₁, d₂ of first and second compressivelayers 120, 122.

In some embodiments, the ion exchanged glass described herein has acompressive layer extending from a surface of the glass to a depth ofcompression of at least about 45 μm, and all ranges and subrangestherebetween, for example in certain embodiments, the depth ofcompression is in a range from about 45 μm up to about 200 μm. The depthof compression, in some embodiments, is in a range from about 0.05t toabout 0.22t and, in some embodiments, up to about 0.20t, where t is thethickness expressed in microns (μm). The compressive stress in someembodiments, has a maximum compressive stress at the surface. Thecompressive layer(s) of the glass, in some embodiments, are under amaximum compressive stress of at least about 500 MPa. In someembodiments, the maximum compressive stress is at least about 700 MPa,and, in other embodiments, at least about 800 MPa when the glass is ionexchanged to a depth of compression of at least about 45 μm. Table 3alists surface compressive stresses (CS) and depths of compression (DOC),determined from surface stress (FSM) measurements, for examples 1-6 inTable 1 and two reference/control samples that were ion exchanged for 1hour in a molten KNO₃ (100% KNO₃ by weight) bath at 410° C. Table 3blists surface compressive stresses (CS) and depths of compression (DOC),determined from surface stress (FSM) measurements, for examples 7-12listed in Table 1 that were ion exchanged at various times andtemperatures in a molten KNO₃ (100% KNO₃ by weight). Table 3c listssurface compressive stresses (CS) and Depths of Compression (DOC)determined for examples 13-18 listed in Table 1. The examples in Table3c were ion exchanged at 430° C. for 8 hours in a molten ion exchangebath comprising 100% KNO₃ by weight. The compressive stress (CS) and DOCwere determined from spectra of bound optical modes for TM and TEpolarization collected via prism coupling techniques. Using the inverseWentzel-Kramers-Brillouin (IWKB) method detailed and precise TM and TErefractive index profiles n_(TM)(z) and n_(TE)(Z) were obtained from thespectra.

In another aspect, a method of ion exchanging a glass is also provided.The method includes ion exchanging a glass, which comprises SiO₂, Al₂O₃,P₂O₅, Na₂O, and optionally at least one of ZnO and at least one alkalineearth oxide, wherein (R₂O (mol %)+RO (mol %))−(Al₂O₃ (mol %)+P₂O₅ (mol%))<0, where R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O and R′O=MgO+CaO+SrO+BaO, in anion exchange bath comprising a potassium salt such as, but not limitedto, KNO₃ at a temperature in a range from about 370° C. to 390° C. for aperiod of up to one hour to form a compressive layer extending from asurface of the glass to a depth of compression of at least about 45 μm.In certain embodiments, the depth of compression is in a range fromabout 45 μm up to about 200 μm and, in other embodiments, up to about300 μm. The depth of compression, in some embodiments, is in a rangefrom about 0.05t to about 0.22t and, in some embodiments, up to about0.20t, where t is the thickness expressed in microns (μm). The ionexchange bath may contain other salts, such as, for example, NaNO₃, ormay contain only, or consist essentially of, KNO₃. The ion exchange bathis maintained at a temperature in a range from about 370° C. to 390° C.throughout the process. The compressive layer(s) of the glass, in someembodiments, include a compressive stress of at least about 500 MPa. Insome embodiments, the maximum compressive stress is at least about 700MPa, and, in other embodiments, at least about 800 MPa.

In some embodiments, the glass may be ion exchanged using a two-step ordual ion exchange (DIOX) process in which the glass is immersed in afirst ion exchange bath followed by immersion in a second ion exchangebath, wherein the composition of the first ion exchange bath differsfrom that of the second ion exchange bath. In addition, the temperaturesand immersion times in the first and second ion exchange baths maydiffer from each other. The DIOX process may be used to achieve a deepdepth of compression and provide an increased maximum compressive stressor compressive stress “spike” at the surface. In one non-limitingexample, the glass is ion exchanged at 450° C. for about 20 hours in afirst bath containing about 30% NaNO₃ and about 70% KNO₃ by weight andthen ion exchanged at about 360° C. for about 12 minutes in a secondbath containing about 5% NaNO₃ and about 95% KNO₃ by weight.

TABLE 1 Compositions, strain points, anneal points, softening points,and coefficients of thermal expansion of glasses. Example 1 2 3 4 5 6SiO₂ 60.69 60.77 60.81 57.58 57.69 57.52 Al₂O₃ 13.96 14.01 14.05 16.9816.96 16.97 P₂O₅ 7.72 7.64 7.60 7.75 7.70 7.81 Na₂O 15.55 14.57 13.5815.60 14.63 13.69 K₂O 1.92 2.87 3.81 1.93 2.89 3.85 MgO SnO₂ (P₂O₅ +R₂O)/Al₂O₃ 1.804 1.790 1.780 1.489 1.487 1.494 CTE (0-300° C.) 92 94.194.3 91.3 92.3 93.2 Strain Point (° C.) 553 545 548 590 586 588 AnnealPoint (° C.) 610 601 605 650 646 648 Softening Point (° C.) 893.9 902.2899.2 940.1 944.6 948.1 Example 7 8 9 10 11 12 SiO₂ 62.97 65.07 64.9562.81 62.93 63.00 Al₂O₃ 12.06 10.06 11.10 13.08 12.09 11.08 P₂O₅ 7.487.44 6.48 6.55 6.49 7.49 Na₂O 13.62 13.57 13.58 13.63 14.60 14.58 K₂O3.80 3.78 3.82 3.84 3.82 3.77 MgO 0.01 0.01 0.01 0.02 0.02 0.01 SnO₂0.03 0.03 0.03 0.03 0.03 0.03 (P₂O₅ + R₂O)/Al₂O₃ 2.064 2.465 2.151 1.8372.060 2.332 CTE (0-300° C.) 95 98 95.7 94.2 98.9 100.5 Strain Point (°C.) 527 589 550 544 536 546 Anneal Point (° C.) 580 642 599 600 584 593Softening Point (° C.) 877.2 934.1 893.8 898.1 868.8 896.1 Example 13 1415 16 17 SiO₂ 63.61 62.60 62.68 62.61 62.56 Al₂O₃ 12.91 13.89 12.9612.93 13.94 P₂O₅ 5.87 5.88 5.81 5.88 5.86 Na₂O 13.69 13.69 14.65 13.7014.68 K₂O 3.87 3.89 3.86 3.89 2.92 MgO 0.01 0.01 0.01 0.96 0.01 SnO₂0.03 0.03 0.03 0.03 0.03 (P₂O₅ + R₂O)/Al₂O₃ 1.814 1.689 1.877 1.8161.683 CTE (0-300° C.) 94.6 94.1 98 94.9 92.9 Strain Point (° C.) 537 559Anneal Point (° C.) 588 615 Softening Point (° C.) 896.7 918.3 906Example Reference 18 glass A SiO₂ 62.67 58.18 Al₂O₃ 13.94 15.32 P₂O₅4.83 6.55 Na₂O 14.65 16.51 K₂O 3.87 2.28 MgO 0.01 1.07 SnO₂ 0.03 0.10(P₂O₅ + R₂O)/Al₂O₃ 1.674 58.18 CTE (0-300° C.) 97.4 97.3 Strain Point (°C.) 561 556 Anneal Point (° C.) 615 609 Softening Point (° C.) 897.4 884

TABLE 2 Physical properties, including densities, 35 kP temperatures,160 kP temperatures, zircon breakdown temperatures T^(breakdown), zirconbreakdown viscosities, liquidus temperatures and viscosities, refractiveindices (RI), Poisson's ratios, shear moduli, Young's moduli, and stressoptical coefficients (SOC) for glasses listed in Table 1. Example 1 2 34 5 6 35 kP Temp T^(35 kP) (° C.) 1219 1229 1226 1248 1262 1270 160 kPTemp T^(160 kP) (° C.) 1126 1134 1133 1159 1172 1179 Zircon BreakdownTemp (° C.) Zircon Breakdown Viscosity (kP) Liquidus Temp (° C.)Liquidus Viscosity (×10⁶ P) Density (RT) 2.399 2.399 2.399 2.406 2.4062.405 RI 1.4866 1.4865 1.4865 1.4889 1.4889 1.4889 Poissons Ratio 0.210.216 0.212 0.212 0.219 0.201 Shear Modulus (Mpsi) 3.71 3.72 3.71 3.793.8 3.8 Youngs Modulus (Mpsi) 8.98 9.06 9 9.2 9.27 9.13 Example 7 8 9 1011 12 35 kP Temp T^(35 kP) (° C.) 1168 1184 1220 1170 160 kP TempT^(160 kP) (° C.) 1082 1092 1124 1080 Zircon Breakdown Temp (°C.) >1277 >1278 >1308 Zircon Breakdown Viscosity (kP) Liquidus Temp (°C.) 1040 925 895 Liquidus Viscosity (×10⁶ P) Density (RT) 2.393 2.3972.39 2.4 2.402 2.394 SOC (nm/mm/Mpa) 3.011 3.098 3.029 3.037 2.996 3.038RI 1.4846 1.4815 1.4844 1.4872 1.4866 1.4839 Poissons Ratio 0.211 0.2080.21 0.208 0.211 0.209 Shear Modulus (Mpsi) 3.68 3.63 3.71 3.75 3.723.64 Youngs Modulus (Mpsi) 8.9 8.77 8.97 9.05 9 8.8 Example 13 14 15 1617 35 kP Temp T^(35 kP) (° C.) 1233 1252 1204 1227 1246 160 kP TempT^(160 kP) (° C.) 1140 1157 1110 1132 1151 Zircon Breakdown Temp (° C.)Zircon Breakdown Viscosity (kP) Liquidus Temp (° C.) Liquidus Viscosity(×10⁶ P) Density (RT) 2.404 2.407 2.411 2.41 2.407 SOC (nm/mm/Mpa) 3.0323.062 3.016 3.009 3.091 RI 1.4882 1.4890 1.4891 1.4892 1.4892 PoissonsRatio 0.21 0.21 0.21225 0.2093 0.21 Shear Modulus (Mpsi) 3.80 3.833.7975 3.8567 3.83 Youngs Modulus (Mpsi) 9.20 9.26 9.205 9.32 9.27Example 18 Reference glass A 35 kP Temp T^(35 kP) (° C.) 1231 1203 160kP Temp T^(160 kP) (° C.) 1135 1115 Zircon Breakdown Temp (° C.) 1210Zircon Breakdown Viscosity (kP) 31.31 Liquidus Temp (° C.) 780 LiquidusViscosity (x10⁶ P) 2464.31 Density (RT) 2.42 2.422 SOC (nm/mm/Mpa) 3.012.95 RI 1.4915 1.4913 Poissons Ratio 0.214 0.205 Shear Modulus (Mpsi)3.8775 3.845 Youngs Modulus (Mpsi) 9.4075 9.266

TABLE 3a Surface compressive stresses (CS) and depths of compression(DOC), determined from surface stress (FSM) measurements, for examples1-6 listed in Table 1 and two reference/control samples (referencesample A composition is given in Table 1; reference sample B compositionis 57 mol % SiO₂, 0 mol % B₂O₃, 17 mol % Al₂O₃, 7 mol % P₂O₅, 17 mol %Na₂O, 0.02 mol % K₂O, and 3 mol % MgO) that were ion exchanged for 1hour in a molten KNO₃ (100% KNO₃ by weight) bath at 410° C. Example 1 23 4 5 6 410° C. 1 h CS (MPa) 677 647 602 794 766 700 DOL (μm) 56 62 6451 52 54 Control B A CS (MPa) 945 823 DOC (μm) 26 42

TABLE 3b Surface compressive stresses (CS) and depths of compression(DOC), determined from surface stress (FSM) measurements, for examples7-12 listed in Table 1 that were ion exchanged at various times andtemperatures in a molten KNO₃ (100% KNO₃ by weight). Example 7 8 9 10 1112 390° C. 1 h CS (MPa) 788 726 808 877 880 801 DOC (μm) 51 45 45 53 4846 390° C. 2 h CS (MPa) 768 726 808 853 864 795 DOC (μm) 70 59 61 73 6662 430° C. 2 h CS (MPa) 705 685 759 794 788 727 DOC (μm) 110 86 89 105102 92 430° C. 1 h CS (MPa) 502 712 783 560 563 522 DOC (μm) 78 63 69 8377 73

TABLE 3c Surface compressive stresses (CS) and depths of compresion(DOC), from spectra of bound optical modes for TM and TE polarizationcollected via prism coupling techniques and the inverse Wentzel-Kramers-Brillouin (IWKB) method, for examples 13-18 listed in Table 1that were ion exchanged at 430° C. for 8 hours in a molten KNO₃ (100%KNO₃ by weight) ion exchange bath. Example 13 14 15 16 17 18 430° C. 8 hCS (MPa) 373 449 403 463 493 480 DOC (μm) 191 211 243 226 213 229

The glasses disclosed herein may be incorporated into another article,such as an article with a display (or display articles) (e.g., consumerelectronics, including mobile phones, tablets, computers, navigationsystems, and the like), architectural articles, transportation articles(e.g., automotive, trains, aircraft, sea craft, etc.), appliancearticles, or any article that requires some transparency,scratch-resistance, abrasion resistance or a combination thereof. Anexemplary article incorporating any of the glasses disclosed herein isshown in FIGS. 2A and 2B. Specifically, FIGS. 2A and 2B show a consumerelectronic device 5100 including a housing 5102 having front 5104, back5106, and side surfaces 5108; electrical components (not shown) that areat least partially inside or entirely within the housing and includingat least a controller, a memory, and a display 5110 at or adjacent tothe front surface of the housing; and a cover substrate 5112 at or overthe front surface of the housing such that it is over the display. Insome embodiments, the cover substrate 5112 may include any of theglasses disclosed herein.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of the present disclosure and appended claims.

1. A glass comprising: greater than 57 mol % SiO₂; Al₂O₃; 4 mol % to 8mol % P₂O₅; Na₂O; greater than 1 mol % K₂O; and ZnO, wherein (R₂O (mol%)+R′O (mol %))−(Al₂O₃ (mol %)+P₂O₅ (mol %))<0,R₂O=Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O, and R′O=ZnO+MgO+CaO+SrO+BaO, and whereinthe glass is substantially free of lithium.
 2. The glass of claim 1,wherein the glass has a coefficient of thermal expansion of at least92×10⁻⁷° C.⁻¹.
 3. The glass of claim 1, wherein the glass has acompressive layer extending from a surface of the glass to a depth ofcompression of at least 45 μm.
 4. The glass of claim 3, wherein thedepth of compression is in a range from 45 μm up to 200 μm.
 5. The glassof claim 3, wherein the glass has a thickness t and wherein the depth ofcompression is less than or equal to 0.22t.
 6. The glass of claim 3,wherein the compressive layer comprises a compressive stress of at least500 MPa.
 7. The glass of claim 1, wherein the glass has a liquidustemperature T^(L), a 160 kP temperature T^(160kP), a 35 kP temperatureT^(35kP), and a zircon breakdown temperature T^(breakdown), whereinT^(L)<T^(160P) and T^(breakdown)>T^(35kP).
 8. The glass of claim 1,wherein the glass comprises 57 mol % to 67 mol % SiO₂.
 9. The glass ofclaim 1, wherein the glass comprises greater than 60 mol % SiO₂.
 10. Theglass of claim 1, wherein the glass comprises 13 mol % to 16 mol % Na₂O.11. The glass of claim 1, wherein the glass comprises 9 mol % to 18 mol% Al₂O₃.
 12. The glass of claim 1, wherein the glass comprises greaterthan 1 mol % to 5 mol % K₂O.
 13. The glass of claim 1, wherein the glasscomprises: 57 mol % to 67 mol % SiO₂; 9 mol % to 18 mol % Al₂O₃; 13 mol% to 16 mol % Na₂O; and greater than 1 mol % to 5 mol % K₂O.
 14. Theglass of claim 1, further comprising less than 1 mol % MgO.
 15. Theglass of claim 1, wherein the glass is substantially free of MgO. 16.The glass of claim 1, wherein R₂O+R′O is less than 18 mol %.
 17. Theglass of claim 1, wherein the glass is substantially free of B₂O₃.
 18. Aconsumer electronic product, comprising: a housing having a frontsurface, a back surface and side surfaces; electrical componentsprovided at least partially within the housing, the electricalcomponents including at least a controller, a memory, and a display, thedisplay being provided at or adjacent the front surface of the housing;and the glass of claim 1 disposed over the display.
 19. An ion exchangedglass comprising the glass of claim
 1. 20. A consumer electronicproduct, comprising: a housing having a front surface, a back surfaceand side surfaces; electrical components provided at least partiallywithin the housing, the electrical components including at least acontroller, a memory, and a display, the display being provided at oradjacent the front surface of the housing; and the glass of claim 19disposed over the display.